M3 or M4 and INTERACTION

Hello NONMEM users, In the article "Likelihood based approaches to handling data BLQ using NONMWM VI". Ahn, Karlsson, Dunne and Ludden provided nonmem codes (p. 419-421). It seems like if we want to apply INTERACTION approach to M3 and use additive+CV model of error, we need to replace SIG with SQRT(SIG**2+(CV*IPRED)**2) and SIG*ERR(1) with SIG*ERR(1)+IPRED*CV*ERR(2) (without F_FLAG). If we do not want to have the additive component, we need to replace SIG with CV*IPRED and SIG*ERR(1) with IPRED*CV*ERR(2). The same applies to M4. Are there strong objections? Thanks! Regards, Pavel